The basic technique in forming electrodeposited foil has not changed greatly over the years. In this respect, electrodeposited copper foil is generally formed by immersing a rotating drum cathode in an electrolyte solution containing copper ions. An anode formed from one or more arcuate sections of electrolytically conductive material is immersed in the electrolyte solution and positioned adjacent the drum cathode. The anode is formed to have a surface generally conforming to the curvature of the drum cathode to define a uniform inner electrode gap therebetween. Copper foil is formed on the rotating drum cathode by applying a current, having a current density lower than the limiting current density of the electrolyte solution, to the anode and cathode. The electrodeposited foil is continually removed from the drum cathode as it emerges from the electrolyte solution so as to permit continuous foil production.
It is well known in the art that the most important parameter in forming deposited foil of high quality and uniform thickness is that the current density along the inner electrode gap. In this respect, it is necessary that the current density along the inner electrode gap be as consistent and constant as possible to ensure uniform deposition of metal on the drum cathode. The design of the anode assembly surrounding the drum cathode is thus extremely important, and it is critical that a uniform, accurate spacing be established and maintained between the drum cathode and the anode. If the distance between the anode and drum cathode varies from area to another, the cathode's current density in the area of greater distance is less which reduces the deposition of metal in that area. In another respect, the conductive characteristics, i.e., the current carrying characteristics, of the anode material are also important in establishing a uniform current density across the surface thereof.
In an effort to maintain a uniform, inner electrode gap, attempts have been made to utilize an anode material which will not react with the electrolyte solution, such as titanium, stainless steel, chromium, columbium, tantalum, or an alloy thereof. These metals are generally non-reactive with electrolyte fluid and provide the dimensional stability desired to maintain a uniform electrode gap. These materials are, however, relatively poor electrical conductors (as compared to copper), and anode designs known heretofore do not lend themselves to utilization of these materials. In this respect, anode designs known heretofore generally utilize thick, elongated bars or thick, flat plates which are bent or formed to have a curved configuration conforming to the curvature of the drum cathode. These bars or plates are fairly massive so as to maintain dimensional stability under the considerable hydraulic pressure exerted thereagainst by the rotating drum cathode, and are typically electrically charged along the peripheral edges thereof. Because of the poor electrical properties of such materials, considerable electrical power is required to charge such components; yet, current distribution throughout the plates or bars may be poor due to the resistance of such materials. This may result in uneven current densities along the surface of the anode and inefficiency due to the loss of electrical power through heat loss.
The present invention provides an anode assembly which utilizes thin, rigid preformed anode plates formed of an inert conductive metal, which plates are mounted onto an anode grid formed of a highly conductive metal which is encased in a protective cladding.